WHITE BALANCE

EXTRACT TAKEN FROM THE ART OF PHOTOGRAPHY

The colour of light is measured by temperature on the Kelvin scale.

The scale shows the effects of temperature of the light on its tone
or hue.

Midday light is deemed as " white light " or neutral light. Dawn or
dust are deemed to be " warm" light as they are of red tones.
Shaded or overcast light are measured as " cool" light as the
hue are blue.

The kelvin registers them as white light as 5000k, warm light
below 2000k and cool light above 6500k.

To compensate for the tone of light, white balance can be adjusted
to try to bring light back to the daylight temperature of
5500k ( or neutral light) Therefore red light such as tungsten
or candle light can be toned down by adding blue white
balance or using a blue filter ( 80a) for a film camera

Cool light such as and overcast day can be warmed up by
adding red tones via white balance or using a
warming up filter ( 81a-81c)



The below chart shows the colour of light and its tonal
effects for both natural and artificial light.

White Balance

As explained light is made up of many combinations of colour and tone
The camera captures this light by colour tones ( red, green, blue)
colour pixels. The objective of the photographer is to capture the
white tone of light so will need to enhance the way the camera
captures the colour tone omitting from the scene being photographed.

As film photography when the photographer would use external filters

Example of colour capture and compensation

As described above the colour of tungsten light has a
low Kelvin reading and is seen by camera as red or
hot it needs to be compensated by adding blue
into the image.

The above image was taken in night light conditions. The scene
was lit by large tungsten street lights. The image was taken
without any colour balance compensation.

I have adjusted the colour temprature in raw
converter to " cool " the image tone to
move the colour tone back to white.

When taking the image the photographer can
choose various was of managing colour capture.

The camera has a facility to manage the tone of
the pixels by pre set white balance settings


They are

SHADE- as cloudy or shaded light is filtered by
cloud cover this light is read by the camera as
" COOL " and is very blue so to compensate
for this the shade setting adds red into the image
to add warmth into the image.



















The original shade image without compensation which
has a clear cool tone.

The above image is processed and colour balanced to shade
which has added red tone to counter balance the blue colour
of the cloudy sky.

INCANDESCENT- as the Tungsten example above
the camera reads artificial light as red and as the light
temperature is hot the image needs to be cooled


FLORESCENT-  The kelvin reading for this light is
3200k and can been seen as green light by the camera.

The above image was taken in the Greenwich tunnel which is
is solely lit by florescent lights. This means the image has a green
hue.

The colour adjusted image adds blue and magenta into the image
to counter balance the green tone.


AUTO.  The photographer can select auto which means the camera
can read the colour tone and temperature from the scene and then
select an average white balance compensation. As setting an average
exposure this is only ever going to be as good as the source of light
falling onto the camera and you could have mixed lighting's conditions
which means you could have some area on the image in shade and
some in light. This is a good tool to use if you are taking a lot of images
on the same day, such as images for an event and you need to have
may be going in different conditions throughout the day.

the above image was taken on an overcast day.
The above image was set at AUTO white balance
and the image has a blue tone to the overall colour
of the image.

The second image shows white balance pre set to the
cloudy sky and the camera has adjusted the image
to warm up the colour tones to compensate for the
cool, cloudy sky.

It clearly shows that AUTO takes an average view
and it is preferable to pre set the white balance.


PRESET white balance.

The photographer can pre set the white balance by
using the cameras TTL light meter to read the
temperature of the scene. This is good way of
ensuring that the camera white balance is set
to the correct colour tones and  is inappropriate
to the temperature of the light avail. The best result
would to read the light back into the camera off a white
card and this would be the ideal "white" tone the camera
can use.

The first image was taken on a daylight setting and it clearly has

a very "cool" tone to the image. The second image was then shot

was taken with the white balance set to the very cloudy rainy

conditions.

Overcast cloudy skies have a kelvin reading of 6500-7500k

which is seen as blue light by the camera. The camera reading

of the sky has indicated to the camera that the white balance

needs to be warmer to compensate for the cook sky.

The second shot is therefore warmer and the blue tones have

been reduced and red has been added to the image

Conclusion

Light that hits the camera will be read by the camera 

by its colour temperature. Hot light is seen as red by 

the camera and cool light as blue. It is therefore important

for the camera to neutralize these colours to try to 

reproduce "white" light seen by the eye of the photographer.

To do this the photographer will need to balance the

white tones captured in the image.

My overall preference will be to pre set the white balance

to the overall lighting conditions. I think it is important to

marry the white to the light that is falling on the scene. I

usually do not read the light from a white card but will

use this technique in the field and will record the results.